in analytical chemistry, a technique for identifying and quantitatively analyzing the chemical composition of substances by observing the thermal behaviour of a sample as it is heated (heat). The technique is based on the fact that as a substance is heated, it undergoes reactions and phase changes that involve absorption or emission of heat. In DTA the temperature of the test material is measured relative to that of an adjacent inert material. A thermocouple imbedded in the test piece and another in the inert material are connected so that any differential temperatures generated during the heating cycle are graphically recorded as a series of peaks on a moving chart. The amount of heat involved and temperature at which these changes take place are characteristic of individual elements or compounds; identification of a substance, therefore, is accomplished by comparing DTA curves obtained from the unknown with those of known elements or compounds. Moreover, the amount of a substance present in a composite sample will be related to the area under the peaks in the graph, and this amount can be determined by comparing the area of a characteristic peak with areas from a series of standard samples analyzed under identical conditions. The DTA technique is widely used for identifying minerals and mineral mixtures.